Wireless devices for communication such as terminals are also known as e.g. User Equipments (UE), mobile terminals, wireless terminals and/or mobile stations. Terminals are enabled to communicate wirelessly in a cellular communications network or wireless communication system, sometimes also referred to as a cellular radio system or cellular networks. The communication may be performed e.g. between two terminals, between a terminal and a regular telephone and/or between a terminal and a server via a Radio Access Network (RAN) and possibly one or more core networks, comprised within the cellular communications network.
Terminals may further be referred to as mobile telephones, cellular telephones, laptops, or surf plates with wireless capability, just to mention some further examples. The terminals in the present context may be, for example, portable, pocket-storable, handheld, computer-comprised, or vehicle-mounted mobile devices, enabled to communicate voice and/or data, via the RAN, with another entity, such as another terminal or a server.
The cellular communications network covers a geographical area which is divided into cell areas, wherein each cell area being served by a base station, e.g. a Radio Base Station (RBS), which sometimes may be referred to as e.g. “eNB”, “eNodeB”, “NodeB”, “B node”, Base Transceiver Station (BTS), or AP (Access Point), depending on the technology and terminology used. The base stations may be of different classes such as e.g. macro eNodeB, home eNodeB or pico base station, based on transmission power and thereby also cell size. A cell is the geographical area where radio coverage is provided by the base station at a base station site. One base station, situated on the base station site, may serve one or several cells. Further, each base station may support one or several communication technologies. The base stations communicate over the air interface operating on radio frequencies with the terminals within range of the base stations. In the context of this disclosure, the expression Downlink (DL) is used for the transmission path from the base station to the mobile station. The expression Uplink (UL) is used for the transmission path in the opposite direction i.e. from the mobile station to the base station.
In 3rd Generation Partnership Project (3GPP) Long Term Evolution (LTE), base stations, which may be referred to as eNodeBs or even eNBs, may be directly connected to one or more core networks.
UMTS is a third generation mobile communication system, which evolved from the GSM, and is intended to provide improved mobile communication services based on Wideband Code Division Multiple Access (WCDMA) access technology. UMTS Terrestrial Radio Access Network (UTRAN) is essentially a radio access network using wideband code division multiple access for terminals. The 3GPP has undertaken to evolve further the UTRAN and GSM based radio access network technologies.
3GPP LTE radio access standard has been written in order to support high bitrates and low latency both for uplink and downlink traffic. All data transmission is in LTE controlled by the radio base station.
Device-to-Device Communication in Cellular Spectrum
Device-to-device (D2D) communications in cellular spectrum is a relatively new concept that targets scenarios in which communicating parties are in the close proximity of each other. Such communication may be assisted by the cellular network infrastructure when it is available, or it may happen in an adhoc and autonomous fashion in case the cellular network is damaged. Specifically, in 3GPP LTE networks, such LTE Direct communication may be used in commercial applications, such as proximity based social networking or in public safety situations in which first responders need to communicate with each other and with people in the disaster area.
Within the European Conference of Postal and Telecommunications Administrations (CEPT), according to the Electronic Communication Committee (ECC) this type of direct communication is referred to as Direct Mode Operation (DMO) that is recognized as an important part of the European Public Protection and Disaster Relief (PDDR) broadband system. Power control algorithms for DMO are an important part of technical solutions for PDDR systems.
The first step in the establishment of a D2D link is that the devices discover the presence of their peer. During the discovery process, one device is assumed to be in D2D slave role, and the other user equipment in D2D master role. To implement peer discovery, the D2D master device broadcasts signals, indicating its capability to provide certain service, and the D2D slave device tries to discover the D2D master device which may provide a required service. These signals that the master device broadcasts are referred to as beacon signals. Note that a single device may play both roles, i.e. master and slave in different occasions, or even simultaneously.
National Security and Public Safety (NSPS) and Adhoc Communications
The 3GPP has recently started work on standardizing technology, that may be used in NSPS as well as regular commercial cellular services, see http://www.3gpp.orq/Public-Safety. The main business driver for using a common technology for both public safety and commercial use cases lies in the economy of scale of both network and end user equipments thereby offering advantages to both the cellular and public safety communities. However, developing a common technology for these two types of applications implies new technical requirements, such as solutions for radio resource management, interference handling and in particular power and rate control.
Power and Rate Control in Existing Cellular and Adhoc Networks
Existing power control algorithms typically aim at balancing the Signal-to-Interference-plus-Noise-Ratio (SINR) at a receiver. For example, an existing 3GPP LTE uplink power control algorithm compensates for the path loss of cell edge users allowing wireless devices far away from the base station to transmit with a somewhat higher power than wireless devices close to the base station.
Although in practice very seldom used, existing adhoc, distributed, algorithms allow wireless devices to iteratively find transmit power levels such that the SINR values at various receivers tend to become similar, even when the topology of transmitters-receivers is much more complex than the traditional cellular star topology. These algorithms are known by the skilled person as the Foschini-Miljanic type of algorithm, see G. J. Foschini, Z. Miljanic. “A simple distributed autonomous power control algorithm and its convergence”, IEEE Trans. on Vehicular Technology, November 1993, or Zander type of algorithm, see J. Zander, “Distributed Cochannel Interference Control in Cellular Radio Systems”, IEEE Trans. on Vehicular Technology, August 1992.
Rate control is a fundamental means in existing cellular technologies to adaptively adjust data transmission rates by employing Adaptive Modulation and Coding (AMC) schemes. Rate control and AMC, in LTE in the form of Modulation and Coding Scheme (MCS) selection, are typically controlled or assisted by a base station and appropriate signaling.
In NSPS scenarios, a cellular network may become partially damaged or dysfunctional, but a basic requirement is that communication between wireless devices such as user equipments (UEs) in the proximity of each other should be facilitated. When UEs are under cellular network coverage, the cellular network controls their transmit power and manages interference, but when UEs get outside of cellular network coverage or the cellular network becomes unable to control the UE transmit power, a basic problem is for the UEs to exercise power control and rate adaptation.
The UEs do not know what transmit powers to set when they get outside network coverage, including the situation in which some of the communicating UEs are under network coverage and some are outside network coverage.
Further, the UEs do not know how to adjust their transmit power level and control the rate such that UEs both outside and within network coverage should be able to communicate and keep the caused interference under tolerable limits.
Since existing technology for power and rate control either assumes cellular network assistance or comprises some predefined or preconfigured transmit rates and/or SINR targets, the cellular network have a problem to appropriately set the transmit power for cellular UEs when these get outside cellular network coverage. The root cause for this is that without some control entity or pre-configuration, the UEs cannot know what SINR target and corresponding power level and transmit rate they should set. Although some form of pre-configuration may be employed, a single preconfigured transmit power level would be inappropriate for UEs in different situations. A problem is that the distance between communicating UEs may vary between a large range, from a few centimeters up to several hundreds of meters, within or outside network coverage.
This basic problem leads to various negative consequences in mixed cellular and adhoc environments such as:                If UEs try to achieve a too high SINR at their respective receivers, they may cause extremely high interference at other receivers in their close proximity;        If UEs aim at too low SINRs, their feasible communication rates may be much lower than what would be feasible with some higher SINR values;        If a UE under cellular coverage communicates with a UE outside network coverage, the two UEs may use incompatible power and rate control rules leading to low communication rates and high interference between cellular and adhoc UEs.        
WO 02/003567 A3 discloses a method for Adaptive Power Control for Wireless Networks. It generally aims at reducing mobile nodes' power consumption and achieving lower SINR. A distributed algorithm is disclosed for this purpose. However, the distributed algorithm is not optimal.
U.S. Pat. No. 7,899,483 B2 discloses a method and system for Performing Distributed Outer Loop Power Control in Wireless Communication Networks: This document discloses a method that iteratively adjusts the SINR targets in an ad-hoc network. in this method and system the main focus is on an architecture with one Receiving Node and Multiple Transmitter Nodes. However, this method is not optimal.